Described below is an electrical drive,
wherein the drive has a motor and a motor control for the motor,
wherein the motor control has a DC circuit and a switching device,
wherein a back-up capacitor is disposed in the DC circuit,
wherein the DC circuit is connected to a power supply network for feeding energy into the back-up capacitor and the motor is able to be connected to the back-up capacitor via the switching device,
wherein the motor has a stator and a rotor supported rotatably relative to the stator,
wherein the rotor is connected to a spring device by which a restoring force can be applied to the rotor in the event of it being deflected from its idle position,
wherein a control device controlling the switching device for the motor, in the event of energy being fed into the back-up capacitor from the power supply network, activates switching elements of the switching device, as a function of a required deflection of the rotor prespecified to the control device from outside, such that an actual deflection of the rotor is adjusted to the required deflection.
An electrical drive of the type described above is known from WO 2005/119 898 A2.
Spring-loaded drives are often used as drives for valves and flaps in order to guarantee that the valve or flap is moved to a defined position in the event of a failure of the power supply network.
Negative effects can occur when the spring restores the rotor. In particular this can result in a mechanical collision of the restored element which can lead under extreme conditions to mechanical damage. Furthermore electrical energy is generated when the rotor is restored, which must be accommodated and dealt with by the motor control.
In WO 2005/119 898 A2 the motor is embodied as a brushless DC motor. In WO 2005/119 898 A2, to avoid the above problems, it is proposed that two of three windings of the motor be short-circuited through pulse width modulation by the converter and thereby the rotor be moved at a restricted speed into its idle position.
The teaching of WO 2005/119 898 A2 only resolves the above-mentioned problems partly. In particular impact of the valve or flap is avoided. However a high short-circuit current arises which must be dealt with by the motor and by the switching device. Furthermore the voltages occurring in the motor must be dealt with by the switching device.